1. Field of the Invention
The present invention relates to the field of wireless communications.
2. Description of Related Art
In a conventional wireless communications network, such as a cellular or a Personal Communication System (PCS) network, a base station acts as an interface between a subscriber""s mobile-telephone (xe2x80x9cmobilexe2x80x9d) and a mobile services switching center (MSC) to exchange control information and traffic between the mobile and the MSC. The MSC in turn serves as an interface between separate network base stations, as well as between the wireless network and a separate network, such as the public switched telephone network (PSTN).
Wireless networks typically provide two types of xe2x80x9cchannelsxe2x80x9d: traffic channels for carrying voice frequency traffic, and control channels for carrying control information used by a base station and/or a MSC to set up and monitor calls and manage handoffs between base stations as the mobile moves through adjacent cells. Depending on the type of wireless network employed, the plurality of channels which enable a single base station to efficiently serve numerous subscribers in a local geographic area are realized, for example, by dividing a licensed frequency band (xe2x80x9clicensed spectrumxe2x80x9d) into multiple frequency channels (e.g., Frequency Division Multiple Access-FDMA), assigning time slots (e.g., Time Division Multiple Access-TDMA), assigning unique pseudo-random codes (Code Division Multiple Access-CDMA), etc.
A mobile typically monitors the relative quality of control signals, such as paging or pilot signals (in CDMA networks), transmitted by the surrounding base stations to determine which base station should serve the mobile""s calls, and to control handoffs as the mobile moves between adjacent cells. When setting up a call, the serving base station instructs the mobile, via a control channel, on which traffic channels to transmit and receive.
When one subscriber calls another subscriber in the conventional wireless network described above, the MSC forwards traffic received from a transmitting mobile via the transmitting mobile""s serving base station to the receiving mobile via the receiving mobile""s serving base station. Such traffic routing through at least one base station and the MSC occurs even when the mobiles are in close proximity. Therefore, the conventional wireless communications network uses essentially the same resources for serving calls between subscribers, regardless of their proximity.
The present invention is a wireless communications system and method which enables proximate mobiles to directly communicate, thereby reducing the burden imposed on network resources by calls between subscribers in the same geographic area. The present invention is also a dual-personality mobile which assumes a base station personality to enable mobile-to-mobile communication, thereby transmitting/receiving traffic to/from another mobile at base station transmit/receive frequencies.
In one embodiment, a serving base station for a calling and a called mobile establishes signaling links with the mobiles using designated control channels. When the serving base station recognizes that the calling and called mobiles are served by the same base station or adjacent base stations, the serving base station instructs the calling mobile and/or the called mobile to monitor the other mobile""s control information transmissions. The so-instructed mobile reports the quality of the control information transmitted by the other mobile, for example based on signal-to-interference ratio or bit error rate measurements, to the serving base station.
If the reported quality measurements are adequate, rather than assign separate mobile-base station traffic channels, the MSC initiates mobile-to-mobile communication by having the serving base station instruct either the calling or the called mobile to enter a base station emulating mode. In the base station emulating mode, the dual-personality mobile establishes a mobile-to-mobile traffic link by transmitting/receiving traffic at base station transmit/receive frequencies. During mobile-to-mobile communication, the serving base station continues to control the call via the established signaling links, thereby maintaining billing information and the like.
During mobile-to-mobile communication, the calling and called mobiles measure mobile-to-mobile traffic link quality, and report these quality measurements via the serving base station. When the reported quality measurements indicate a deteriorating mobile-to-mobile traffic link, due for example to mobility, the MSC terminates mobile-to-mobile communication by having the serving base station instruct the base station emulating mobile to resume normal operation (i.e., assigning traffic channels over the network infrastructure and a separate pair of air interface channels for the mobile no longer in the base station emulating mode), thereby handing off traffic communication to the serving base station. If the mobiles later return to suitable positioning, the MSC re-initiates mobile-to-mobile communication by having the serving base station again instruct one of the mobiles to assume a base station personality.
Advantageously, this embodiment of the present invention enables the wireless network to handle a significant number of calls between proximate mobiles, without relying on network infrastructure to support the resulting voice traffic. Therefore, this embodiment is particularly suited to environments in which communicating subscribers are likely to be in close proximity, such as college campuses and work facilities. Moreover, this embodiment of the present invention does not require a mobile-base station traffic channel for both the calling mobile and the called mobile, thereby reducing the number of air interface channels which are reserved for a call between proximate subscribers. The reduced number of air interface channels allows more subscribers to be served with a given amount of licensed spectrum. Since a serving base station continues to control mobile-to-mobile calls, billing information is preserved and handled by the MSC.